Add cppcheck suppression for unused struct member in iomanX_port.h

Author: AKuHAK

src/iomanX_port.h

@@ -167,6 +167,7 @@ typedef struct
     /*24*/ unsigned int hisize;
     /*28*/ unsigned int private_0; // Number of subs (main) / subpart number (sub)
     /*2c*/ unsigned int private_1; // partition size low part
+    // cppcheck-suppress unusedStructMember
     /*30*/ unsigned int private_2; // partition size high part
     /*34*/ unsigned int private_3;
     /*38*/ unsigned int private_4;